netbeans synchronizes its internal clipboard with the system one only when the main window is activated - for performance reasons.
when running in virtual box then netbeans window doesn't get deactivated and activated when copying content to clipboard from some other application so it keeps its stale, cached content.

> Given the last comments here, closing as wontfix.
>
> We should not change the clipboard [polling] policy for performance reasons.
This is not an acceptable answer. There are more options besides "leave it broken" and "poll constantly and kill performance." For example, you can update the clipboard during the "Paste" operation. Yes, it may slow down the intial paste operation, but probably not as much caused by manually deactivating and reactivating the NB window--to say nothing of the productivity cost this issue causes a programmer. A malfunctioning paste is a useless paste.

(In reply to comment #6)
> broken" and "poll constantly and kill performance." For example, you can update
> the clipboard during the "Paste" operation.
that means the paste action would be always enabled, even when there's no clipboard content to paste.

Are yall actually serious about this? Copy/paste doesn't work!
If you're going to half-ass that, then stop updating the bugs and go outside and play. There's no need to continue working on NetBeans or editing the bugs.
In response to paste always being visible, that's better than it NOT WORKING!
Re: performance, someone, somewhere can figure this out. Just because you can't doesn't mean close the bug.